Data transmission method, data transmission system, transmitter and receiver

ABSTRACT

A data transmission method etc. is provided. At a transmitting side, if a frame contains transmission data, frame data containing the transmission data and a calculated error-detecting code is generated. If the frame contains no transmission data, frame data containing neither transmission data nor an error-detecting code is generated. At a receiving side, one or more final bit positions of the frame data are assumed in the frame, transmission data and an error-detecting code are assumed in the frame, and the error-detecting code of the assumed transmission data is calculated. If there is a position where the assumed error-detecting code matches the error-detecting code calculated based on the assumed transmission data, it is decided that the position is the final bit position. Otherwise, it is decided that the frame contains no transmission data or that the received frame data contains an error.

This application claims priority under 35 U.S.C. 119 to PatentApplication No. 2000-351884 filed Nov. 17, 2000 in Japan, the content ofwhich is incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a data transmission method, a datatransmission system, a transmitter and a receiver where variable lengthtransmission data is put into each frame of a fixed time length andtransmitted.

2. Description of the Related Arts

In the data transmission method where information of voice signals andthe like is converted into digital data and transmitted, an amount ofinformation to be transmitted is not always constant in terms of time,but generally may change from time to time.

Accordingly, if the transmission data is divided into frame units eachhaving a fixed time length and each frame consisting of variable numberof bits is transmitted frame by frame to achieve the data transmission,a transmission rate can be varied temporally and necessary informationcan be transmitted efficiently in each frame period. At this time, atransmitter need not conduct useless transmission and hence the powerconsumption of the apparatus can be suppressed to low.

To conduct data transmission with varying transmission rate, normally itis necessary for the receiving side to get information indicating howfast the transmission rate of each frame is by means of some kind oranother. For this purpose, conventionally there have been two methods:one is a method whereby the rate information is transmitted directly aspart of frame data and the receiving side determines the rate on thebasis of this information; and the other is a method where no rateinformation is sent, but the receiving side judges the rate with anerror-detecting code that is added to the transmission data to indicatetransmission quality (for example, CRC: Cyclic Redundancy Check code),called a blind rate detection method (for example, refer toInternational Publication No. WO96/26582 applied by the presentapplicant).

On the other hand, in communication environments where transmissionerrors occur frequently such as data transmission via a radiotransmission path, it is commonly in practice to improve transmissionquality by conducting error correction of the transmission data (FEC:Forward Error Correction). For error-correcting codes anderror-correcting decoding, for example, a convolutional code and maximumlikelihood decoding methods such as Viterbi decoding are used.

In addition, in the method where the receiving side determines the rateby using the error-detecting code that is added to the transmission datato indicate the transmission quality without sending any rateinformation, a decision error rate in determining the rate depends on aword length of the error-detecting code and doesn't decrease below acertain rate-decision error rate (namely, a probability of determiningthat no transmission error exists for an erroneous rate) even if thetransmission error goes down.

On the other hand, in the case where the rate information is sent fromthe transmitting side to the receiving side, if an error occurs duringtransmission, an effective data length in the received frame cannot bejudged and it becomes difficult for the receiving side to reproduce thetransmission data correctly even if no error occurs in the data part.

Therefore, conventionally there has been devised a method whereby therate-decision error rate was improved through the use of the likelihoodinformation at the time of the maximum likelihood decoding and thetransmission rate is allowed to vary, frame by frame, more securelyduring the transmission (for example, refer to International PublicationNo. WO97/50219 applied by the present applicant).

In the above-mentioned WO96/26582 and WO97/50219, described is a methodwhere, in order to improve the rate detection performance at thereceiving side (that is, to reduce the probability of detecting the ratemistakenly), CRC bits that have been conventionally added to the end ofthe transmission data (in this case the position of the CRC bits in theframe depends on the bit length of the transmission data) are arrangedat a fixed position in the frame (for example, at the head of the frame)and transmitted.

FIGS. 1A and 1B are diagrams showing an example of transmission bitarrangement of the conventional scheme.

In the conventional method where the CRC bits are arranged aftertransmission data bits (“conventional postposition”), for example, whena position one bit ahead from the correct rate position is detected,since the codewords at the receiving side goes successively as D1 to D0and C4 to C1, even if no transmission bit error occurs, the decisionresult by CRC shows OK (namely, erroneous detection) with a probabilityof 50 percent. Similarly to this, when a position two bits and threebits ahead from the correct rate position is detected, the decisionresult by CRC indicates OK erroneously with a probability of 25 percentand 12.5 percent, respectively.

To solve such a problem that the probability of detecting the ratemistakenly becomes larger as the assumed position approaches the correctrate position, there was devised a method where the CRC bits arearranged at the head of the frame in the above-mentioned WO96/26582 andWO97/50219. In this method, as shown in FIG. 1B (“preposition” case),since a codeword arrangement at the receiving side is discontinuous asD1, C4 to C1, the above-mentioned problem does not occur and a lowprobability of detecting the rate mistakenly that is determined by theword length of the CRC code can be obtained constantly, from a detectionposition adjacent to the correct position to a detection position remotetherefrom.

However, in order that the transmitting side arranges the CRC bitsalways at the head of the frame, that is, ahead of the transmission dataand transmits, it is essential to store temporarily the whole bits ofthe transmission data in memory until calculation of the error-detectingcode for the transmission data is completed. Such buffer memory becomeslarge in size in proportion to the number of the transmission data bitsof one frame, and when a huge amount of the transmission data is sent,hardware scale of the memory presents a problem.

To solve the problem, a method is disclosed in International PublicationNo. WO00/79720 in which an error-detecting code (CRC bits, for example)is provided after transmission data in such a way that the order of theerror-detecting code bits is the reverse of that of the transmissiondata bits to transmit them.

FIGS. 2A and 2B are diagrams showing examples of the transmission bitarrangements of the conventional scheme and of the scheme according tothe invention disclosed in WO00/79720. As can be understood from thefigures, according to the arrangement of the invention disclosed inWO00/79720 (“new postposition” ), since the codeword arrangement at thereceiving side is discontinuous as D1, D0, C0, there does not occur aproblem in that the probability of detecting the rate mistakenlyincreases as the detection position approaches the correct rate positionand a low probability of detecting the rate mistakenly that isdetermined by the word length of the CRC code can be obtainedconstantly, from a detection position adjacent to the correct positionto a detection position remote therefrom.

Moreover, since the bit arrangement according to the invention disclosedin WO00/79720 is such that CRC is arranged after the transmission data,it is not necessary to provide the buffer for temporarily storing thetransmission data while maintaining the rate detection performance highas mentioned above and hardware can be implemented with a small circuitscale.

Furthermore, in the invention disclosed in WO00/79720, it is possiblethat, considering a case where the number of bits of the transmitteddata becomes zero, if the number of bits of the transmitted data is zeroat the transmitting side, the frame data is generated by considering thepreviously-specified bit pattern to be the error-detecting code. It ispossible that at the receiving side, a position where the number of bitsof the transmitted data becomes zero is also assumed as the final bitposition of the frame data, and if the error-detecting code in the caseof the assumption agrees with the above-mentioned previously-specifiedbit pattern, a decision that the position where the number of bits ofthe transmitted data becomes zero is the final bit position of the framedata is made.

In actual data transmissions, there is a case where the number of bitsof the transmitted data to be sent becomes zero, for example, as asilent interval (namely, an interval when a sender does not speak) inthe case of transmission of voice information, and it is preferable thatthe receiving side conducts the rate detection correctly for variouscases including a case like this (that is, a case where apparenttransmission rate=0) (this is because at the receiving side a decoder ofvoice codec (CODEC) may recognize such an interval as a silent intervaland conduct processing different from that of non-silent intervals, suchas generation of a background noise).

For the previously-specified bit pattern, for example, bits equivalentto the parity bits of the error-detecting code (because of absence ofthe data, bits corresponding to an initial state of the error-detectingcoder; for example, bits all consisting of zeros) may be used. If thenumber of bits of the transmitted data is zero, the transmitting sidetransmits the bits equivalent to the parity bits of the error-detectingcode,(because of absence of the data, only these bits equivalent to theparity bits are error-correcting coded and transmitted). At thereceiving side, the rate detection is conducted for candidate final bitpositions including the final bit position when the number of data bitsis equal to zero (the error detection at this occasion does notnecessitate calculating the error-detecting code for the received data—re-encoding—, and all that is needed is only to compare the receivedparity-bit equivalent bits with the previously-specified bit pattern).Incidentally, if the bits equivalent to the parity bits of theerror-detecting code is used as the previously-specified bit pattern,the need for additionally providing a circuit for generating thepreviously-specified bit pattern can be eliminated.

Although the circuit can be used in common by equalizing the length ofthe bit pattern with that of the parity bits of the error-detecting code(or CRC) that is given when the number of the other data bits is notzero, the length may be different as the need arises.

For the bit pattern, it is necessary to specify previously at least onekind of a pattern, but it may be possible that a plurality of patternsare specified and one of these is used in combination with other purpose(each of various control information is transmitted being mapped witheach bit pattern).

According to the invention disclosed in WO00/79720, however, it isrequired that an error-detecting code (CRC bits, for example) be alwaysprovided even if there is no data to achieve adequate performance duringblind rate detection or rate information itself be transmitted, even ina channel such as a control signal transmission channel that isinappropriate for being used as the reference of an outer looptransmission power control (this is a part of a dual closed looptransmission power control that is combined with an inner looptransmission power control, for maintaining and controlling block orframe error rate quality), that is, a channel that requires no frame(block) error rate calculation.

Overhead required to provide the CRC bits also in a period during whichno data exists decreases transmission efficiency considerably in thecase where information is transmitted intermittently like a controlsignal transmission channel.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to achieve ahigh-quality variable rate data transmission based on high-precisionrate detection while reducing overhead in accordance with the concept ofblind rate detection in which rate information is not transmitted.

To achieve the object, in the first aspect of the present invention,there is provided a data transmission method for placing variable-lengthtransmission data in each frame having a fixed time length to transmitthe frame, comprising the steps of: at a transmitting side, calculatingan error-detecting code of the transmission data in the frame only ifthe frame contains the transmission data; generating frame datacontaining the transmission data and the calculated error-detecting codeof the transmission data if the frame contains the transmission data,and generating frame data that contains neither the transmission datanor the error-detecting code of the transmission data if the frame doesnot contain the transmission data; and transmitting the generated framedata; and at a receiving side, receiving the frame data; determining thetransmission data and the error-detecting code of the transmission databy determining a predetermined position in the received frame data asthe final bit position of the frame data, and calculating anerror-detecting code based on the determined transmission data; decidingthat the frame contains the transmission data if the determinederror-detecting code matches the error-detecting code calculated basedon the determined transmission data, and deciding that the frame datadoes not contain the transmission data or the received frame datacontains an error if the determined error-detecting code does not matchthe calculated error-detecting code; and obtaining the transmission datain the frame based on the result of the decision.

In the second aspect of the present invention, there is provided a datatransmission method for placing variable-length transmission data ineach frame having a fixed time length to transmit the frame, comprisingthe steps of: at a transmitting side, calculating an error-detectingcode of the transmission data in the frame only if the frame containsthe transmission data; generating frame data containing the transmissiondata and the calculated error-detecting code of the transmission data ifthe frame contains the transmission data, and generating frame data thatcontains neither the transmission data nor the error-detecting code ofthe transmission data if the frame does not contain the transmissiondata; and transmitting the generated frame data; and at a receivingside, receiving the frame data; assuming the transmission data and theerror-detecting code of the transmission data by assuming one or morefinal bit positions of the received frame data, and calculating anerror-detecting code based on the assumed transmission data; deciding aposition to be the final bit position of the frame data if there is theposition in the frame where the assumed error-detecting code matches theerror-detecting code calculated based on the assumed transmission dataamong the assumed final bit positions of the frame data, and decidingthat the frame does not contain the transmission data or the receivedframe data contains an error if there is no position where the assumederror-detecting code matches the calculated error-detecting code; andobtaining the transmission data in the frame based on the result of thedecision.

Here, at the transmitting side, the step of generating the frame datamay generate the frame data in which the error-detecting code is placedafter the corresponding transmission data and the bits of theerror-detecting code are arranged in the order that is the reverse ofthe order of the bits of the transmission data.

Here, the data transmission method may further comprise: at thetransmitting side, conducting error-correcting coding of the generatedframe data; and conducting interleaving of the frame data that hasundergone the error-correcting coding; and at the receiving side,conducting deinterleaving of the received frame data; and conductingerror-correcting decoding of the frame data that has undergone thedeinterleaving.

Here, at the transmitting side, the data transmission method may furthercomprise the step of calculating transmission rate informationindicating the number of bits of the transmission data in each frame,and the step of generating the frame data generates the frame datacontaining the calculated transmission rate information.

Here, if the frame contains the transmission data, the length of thetransmission data may be within the range from 1 to X bits, the lengthof the error-detecting code associated with the transmission data may beY bits, and the combination of X and Y may be one of (X, Y)=(8, 8),(244, 12), (4080, 16), and (1048576, 24).

Here, the data transmission method may multiplex variable-lengthtransmission data for channels in a first channel group of one or morechannels and transmission data for channels in a second channel group ofone or more channels into each frame having a fixed time length totransmit the frame, and at the transmitting side, the step ofcalculating the error-detecting code may calculate the error-detectingcode of the transmission data for each channel in the first channelgroup only if the frame contains the transmission data for the channel;the step of generating the frame data may generate, for each channel inthe first channel group, partial frame data containing the transmissiondata for the channel and the calculated error-detecting code of thetransmission data for the channel if the frame contains the transmissiondata for the channel, and may generate, for each channel in the firstchannel group, partial frame data containing neither the transmissiondata for the channel nor the error-detecting code of the transmissiondata for the channel if the frame does not contains the transmissiondata for the channel; and the step of transmitting the frame data maytransmit the whole frame data containing the generated partial framedata for each channel in the first channel group, and at the receivingside, the step of receiving the frame data may receive the whole framedata; the step of calculating the error-detecting code may determine thetransmission data for each channel in the first channel group and theerror-detecting code of the transmission data for the channel bydetermining a predetermined position in the partial frame data for thechannel contained in the received whole frame data as the final bitposition and calculates an error-detecting code based on the decidedtransmission data for the channel; the step of deciding may decide, foreach channel in the first channel group, that the partial frame data forthe channel contains the transmission data for the channel if thedetermined error-detecting code of the determined transmission data forthe channel matches the error-detecting code calculated based on thedetermined transmission data for the channel, and may decide, for eachchannel in the first channel group, that the frame does not contain thetransmission data for the channel or the partial frame data for thechannel contains an error if the determined error-detecting code of thedetermined transmission data for the channel does not match theerror-detecting code calculated based on the determined transmissiondata for the channel; and the step of obtaining the transmission datamay obtain the transmission data for each channel in the first channelgroup in the frame based on the result of the decision.

Here, the data transmission method may multiplex variable-lengthtransmission data for channels in a first channel group of one or morechannels and transmission data for channels in a second channel group ofone or more channels into each frame having a fixed time length totransmit the frame, and at the transmitting side, the step ofcalculating the error-detecting code may calculate the error-detectingcode of the transmission data for each channel in the first channelgroup only if the frame contains the transmission data for the channel;the step of generating the frame data may generate, for each channel inthe first channel group, partial frame data containing the transmissiondata for the channel and the calculated error-detecting code of thetransmission data for the channel if the frame contains the transmissiondata for the channel, and may generate, for each channel in the firstchannel group, partial frame data containing neither the transmissiondata for the channel nor the error-detecting code of the transmissiondata for the channel if the frame does not contains the transmissiondata for the channel; and the step of transmitting the frame data maytransmit the whole frame data containing the generated partial framedata for each channel in the first channel group, and at the receivingside, the step of receiving the frame data may receives the whole framedata; the step of calculating the error-detecting code may assume thetransmission data for each channel in the first channel group and theerror-detecting code of the transmission data for the channel byassuming one or more final bit positions of the partial frame data forthe channel contained in the received whole frame data and calculates anerror-detecting code based on the assumed transmission data for thechannel; the step of deciding may decide, for each channel in the firstchannel group, a position to be the final bit position of the partialframe data for the channel if there is the position where the assumederror-detecting code of the transmission data for the channel matchesthe error-detecting code calculated based on the assumed transmissiondata for the channel among the assumed final bit positions of thepartial frame data for the channel, and may decide, for each channel inthe first channel group, that the frame does not contain thetransmission data for the channel or the partial frame data for thechannel contains an error if there is no position where the assumederror-detecting code of the transmission data for the channel matchesthe error-detecting code calculated based on the assumed transmissiondata for the channel among the assumed final bit positions of thepartial frame data for the channel; and the step of obtaining thetransmission data may obtain the transmission data for each channel inthe first channel group in the frame based on the result of thedecision.

Here, dual closed loop transmission power control comprising inner looptransmission power control and outer loop transmission power control maybe performed for the data transmission between the transmitting side andthe receiving side and one or more channels in the second channel groupmay be used as the reference for the outer loop transmission powercontrol without using channels in the first channel group as thereference.

Here, the relative ratio between error-correcting coding ratios of themultiplexed channels and the relative ratio between transmission powersfor the multiplexed channels may be fixed.

In the third aspect of the present invention, there is provided a datatransmission system for placing variable-length transmission data ineach frame having a fixed time length to transmit the frame, comprising:in a transmitter, means for calculating an error-detecting code of thetransmission data in the frame only if the frame contains thetransmission data; means for generating frame data containing thetransmission data and the calculated error-detecting code of thetransmission data if the frame contains the transmission data, andgenerating frame data that contains neither the transmission data northe error-detecting code of the transmission data if the frame does notcontain the transmission data; and means for transmitting the generatedframe data; and in a receiver, means for receiving the frame data; meansfor determining the transmission data and the error-detecting code ofthe transmission data by determining a predetermined position in thereceived frame data as the final bit position of the frame data, andcalculating an error-detecting code based on the determined transmissiondata; means for deciding that the frame contains the transmission dataif the determined error-detecting code matches the error-detecting codecalculated based on the determined transmission data, and deciding thatthe frame data does not contain the transmission data or the receiveddata contains an error if the determined error-detecting code does notmatch the calculated error-detecting code; and means for obtaining thetransmission data in the frame based on the result of the decision.

In the fourth aspect of the present invention, there is provided a datatransmission system for placing variable-length transmission data ineach frame having a fixed time length to transmit the frame, comprising:in a transmitter, means for calculating an error-detecting code of thetransmission data in the frame only if the frame contains thetransmission data; means for generating frame data containing thetransmission data and the calculated error-detecting code of thetransmission data if the frame contains the transmission data, andgenerating frame data that contains neither the transmission data northe error-detecting code of the transmission data if the frame does notcontain the transmission data; and means for transmitting the generatedframe data; and in a receiver, means for receiving the frame data, meansfor assuming the transmission data and the error-detecting code of thetransmission data by assuming one or more final bit positions of thereceived frame data, and calculating an error-detecting code based onthe assumed transmission data; means for deciding a position to be thefinal bit position of the frame data if there is the position in theframe where the assumed error-detecting code matches the error-detectingcode calculated based on the assumed transmission data among the assumedfinal bit positions of the frame data, and deciding that the frame doesnot contain the transmission data or the received frame data contains anerror if there is no position where the assumed error-detecting codematches the calculated error-detecting code; and means for obtaining thetransmission data in the frame based on the result of the decision.

In the fifth aspect of the present invention, there is provided atransmitter for placing variable-length transmission data in each framehaving a fixed time length to transmit the frame, comprising: means forcalculating an error-detecting code of the transmission data in theframe only if the frame contains the transmission data; means forgenerating frame data containing the transmission data and thecalculated error-detecting code of the transmission data if the framecontains the transmission data, and generating frame data that containsneither the transmission data nor the error-detecting code of thetransmission data if the frame does not contain the transmission data;and means for transmitting the generated frame data.

In the sixth aspect of the present invention, there is provided areceiver for receiving, for each frame having a fixed length, frame datacontaining transmission data and an error-detecting code calculated forthe transmission data if the frame contains the transmission data, andreceiving, for each frame having the fixed length, frame data containingneither the transmission data nor the error-detecting code of thetransmission data if the frame does not contain the transmission data,the receiver comprising: means for receiving the frame data; means fordetermining the transmission data and the error-detecting code of thetransmission data by determining a predetermined position in thereceived frame data as the final bit position of the frame data, andcalculating an error-detecting code based on the decided transmissiondata; means for deciding that the frame contains the transmission dataif the determined error-detecting code matches the error-detecting codecalculated based on the decided transmission data, and deciding that theframe data does not contain the transmission data or the received framedata contains an error if the determined error-detecting code does notmatch the calculated error-detecting code; and means for obtaining thetransmission data in the frame based on the result of the decision.

In the seventh aspect of the present invention, there is provided areceiver for receiving, for each frame having a fixed length, frame datacontaining transmission data and an error-detecting code calculated forthe transmission data if the frame contains the transmission data, andreceiving, for each frame having the fixed length, frame data containingneither the transmission data nor the error-detecting code of thetransmission data if the frame does not contain the transmission data,the receiver comprising: means for receiving the frame data; means forassuming the transmission data and the error-detecting code of thetransmission data by assuming one or more final bit positions of thereceived frame data, and calculating an error-detecting code based onthe assumed transmission data; means for deciding a position to be thefinal bit position of the frame data if there is the position in theframe where the assumed error-detecting code matches the error-detectingcode calculated based on the assumed transmission data among the assumedfinal bit positions of the frame data, and deciding that the frame doesnot contain the transmission data or the received frame data contains anerror if there is no position where the assumed error-detecting codematches the calculated error-detecting code; and means for obtaining thetransmission data in the frame based on the result of the decision.

According to the above-described configuration, high-quality variablerate data transmission can be achieved based on high-precision ratedetection while reducing overhead in accordance with the concept ofblind rate detection in which rate information is not transmitted.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are diagrams showing example of transmission bitarrangements of the conventional scheme;

FIGS. 2A and 2B are diagrams showing example of the transmission bitarrangement of the conventional scheme and of the transmission bitarrangement according to the present invention;

FIGS. 3A and 3B are block diagrams showing examples of configurations ofa transmitter and a receiver in a first embodiment according to thepresent invention;

FIGS. 4A, 4B and 4C are diagrams showing examples of frameconfigurations of the transmission data in the first embodimentaccording to the present invention;

FIG. 5 is a diagram illustrating a processing example of an interleaverin the first embodiment according to the present invention;

FIG. 6 is a diagram showing an example of a frame configuration of thetransmission data in the first embodiment according to the presentinvention;

FIG. 7 is a diagram showing an example of a decoded data sequence at thetime of the maximum likelihood decoding in the first embodimentaccording to the present invention;

FIG. 8 is a flowchart of a processing example of rate decision in thefirst embodiment according to the present invention;

FIG. 9 is a diagram showing relationship between FIGS. 9A and 9B;

FIGS. 9A and 9B are flowcharts of another processing example of ratedecision in the first embodiment according to the present invention;

FIGS. 10A and 10B are block diagrams showing examples of theconfigurations of the transmitter and the receiver in a secondembodiment according to the present invention;

FIGS. 11A, 11B and 11C are diagrams showing examples of the frameconfigurations of the transmission data in the second embodimentaccording to the present invention;

FIG. 12 is a flowchart of a processing example of rate decision in thesecond embodiment according to the present invention;

FIGS. 13A, 13B and 13C are diagrams showing examples of the frameconfigurations of the transmission data in the case of the “postpositionand same order”);

FIGS. 14A, 14B and 14C are diagrams showing examples of the frameconfiguration of the transmission data in the case of the “preposition”;

FIGS. 15A and 15B are diagrams showing examples where frame memory anderror-detecting code memory are added to the configuration of the“preposition” case.

FIG. 16 is a diagram showing an example in which transmission data fortwo channels is contained in one frame; and

FIG. 17 is a diagram showing a frame in which two sets of transmissionrate information shown in FIG. 16 are combined into one transmissionrate information.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Hereafter, preferred embodiments to implement the present invention willbe described in detail with reference to the drawings.

(First Embodiment)

FIGS. 3A and 3B show examples of block constructs of a transmitter and areceiver in a first embodiment of the present invention.

In FIGS. 3A and 3B, a transmission data sequence applied to a terminal 1is sent both to an error-detecting coder 4 and a multiplexer 6. Theerror-detecting coder 4 calculates an error-detecting code (CRC paritybits (CRC bits) in this embodiment) for one frame of transmission dataonly if the frame contains the transmission data. In this embodiment,the word length of the CRC bits is a fixed length.

In this embodiment, the sum of the length of the transmission data andthe length of the error-detection code (CRC bits) in one frame is 4096bits maximum. The length of the error-detecting code is 16 bits. Thus,the length of the transmission data is 0 (when there is no data) or avalue in the range from 1 to 4080 bits. According to this embodiment,the error-detecting code is not sent when there is no transmission datato reduce overhead and the length of the error-detecting code isincreased correspondingly, thereby enabling higher-precision ratedetection (that is, high-quality variable rate transmission). Othervalues may be set as the maximum length of the transmission data andlength of the error-detecting code. For example, the maximum length ofthe transmission data may be 8, 244, or 1048576 bits and the length ofthe corresponding error-detecting code may be 8, 12, or 24 bits,respectively.

Then, the multiplexer 6 arranges the error-detecting code (CRC bits)calculated by the error-detecting coder 4 after the transmission data ifthe frame contains the transmission data. Here, the bits of theerror-detecting code are arranged in the opposite (reverse) order to thetransmission data. In this embodiment, the error-detecting coder 4outputs the error-detecting code bites in the opposite order to normaloutput.

In this embodiment, to conduct the error-correcting coding with aconvolutional code, the multiplexer 6 further adds tail bit(s) that willbe necessary for the error-correcting decoding to the transmission dataand the error-detecting code and outputs them sequentially frame byframe. The tail bit may be added by an error-correcting coder 8.

The multiplexer 6 outputs no transmission data, error-detecting code,nor tail bit if the frame contains no transmission data.

FIGS. 4A, 4B and 4C shows examples of the data sequence outputted fromthe multiplexer 6. FIG. 4A shows the case where the transmission rate ofthe transmission data (simply indicated as “data” in FIGS. 4A and 4B) isthe maximum and FIGS. 4B and 4C show the case where the transmissionrate is below the maximum rate. When transmission is conducted at atransmission rate below the maximum rate, a blank time period (timeperiod without data) is produced in the frame. FIGS. 4A and 4B showframes containing transmission data and FIG. 4C shows a frame withouttransmission data. The length of the transmission data placed in eachframe varies with time and therefore the data sequence outputted fromthe multiplexer 6 will be as shown in FIG. 4A in a time period, as shownin FIG. 4B in another period, and as shown in FIG. 4C in yet anotherperiod, for example.

The data sequence outputted from the multiplexer 6 undergoesconvolutional coding in the error-correcting coder 8 and sent to aninterleaver 10 for interleaving. The convolutional coding is notconducted if the frame contains no transmission data.

FIG. 5 shows an example of the interleaving by the interleaver 10. Thedata sequence of one frame is outputted in a direction different from adirection in which the data is inputted, that is, the transmission datainputted in a line direction is outputted in a column direction.Incidentally, as for another example of the interleaving, theinterleaving processing described in Japanese Patent Application No.11-129056 applied by the present applicant can be enumerated. The datasequence outputted from the interleaver 10 is written into s framememory 12.

FIG. 6 shows an example of the frame configuration of the data sequenceobtained from the frame memory 12. The data interval corresponding tothe column of the interleaver 10 is called a slot, and here it isassumed that one slot is composed of N bits and one frame is composed ofM slots. The number of bits of one frame becomes N×M bits.

The output data sequence of the frame memory 12 is modulated by a radiocircuit 14 and transmitted through an antenna 16. Here, for modulationschemes, for example, a spread spectrum modulation scheme, a QPSKmodulation scheme, etc. are used. In addition, it is specified that nomodulation is conducted at a data position corresponding to blank datain the slot. According to the foregoing, the data consisting of variablenumber of bits is made to be transmitted in a constant frame time.

Next, in the receiver, the received signals fed from an antenna 20 isdemodulated by a radio circuit 22 and then inputted into a deinterleaver24 sequentially. The deinterleaver 24 has a memory in it and conductsthe interleaving in such a procedure that inputting into and outputtingfrom the interleaver 10 at the transmitting side are reversed, that is,writing the data into the memory for each column (each slot) and readingthe data for each line. Through such operations as these, an originaldata sequence of one frame is reproduced and the coded transmission datasequence and the error-detecting code are revealed. The interleaving andthe deinterleaving mentioned just above are intended to enhance an errorcorrection effect even further by preventing burst errors as detected inconsecutive data bits.

The deinterleaved data sequence is sent to an error-correcting decoder26 and undergoes the error-correcting decoding by the maximum likelihooddecoding method, and the decoded data sequence is separated into theerror-detecting code and the data sequence by a demultiplexer 28, andthe error-detecting code is inputted into a comparator 34.

On the other hand, the data sequence is outputted from a terminal 2 asreceived data and at the same time inputted into an error-detectingcoder 30. At the error-detecting coder 30, the inputted data sequenceundergoes the same error-detecting coding as that of the transmitteragain. The error-detecting code obtained by re-coding is compared withthe error-detecting code so separated, code-bit by code-bit, by thecomparator 34, and if all the code bits are found to agree with eachother, a coincidence signal is outputted. In addition, since theerror-correcting code bits in the received frame are in a reverse orderto the normal case, the error-detecting coder 30 in this embodimentoutputs the error-correcting code bits in a reverse order to the normalcase.

Here, the error-correcting decoding and the calculation of theerror-detecting code are conducted, frame by frame, by successivelyassuming the final bit position of transmittable frame data. At thisoccasion, the error-correcting decoder 26 sends likelihood informationfor a decoding result up to each of the assumed final bit positions to arate decision circuit 36, and the rate decision circuit 36 decides thefinal bit position, namely, the transmission rate of the frame on thebasis of this likelihood information and the coincidence signal of theerror-detecting codes.

FIG. 7 shows an example of the decoded data sequence at the time of themaximum likelihood decoding, and FIG. 8 shows an example of theprocessing of rate decision (algorithm). Here, for the maximumlikelihood decoding, Viterbi decoding is assumed.

First, after Viterbi decoding starts, regarding a plurality of decodeddata sequences each of which still remains in each state (in the exampleof FIG. 7, K pieces of the decoded data sequences that reach the states1 to K) at the assumed final bit position (in the example of FIGS. 7 and8, the position #L), the likelihoods with respect to the transmissiondata sequence of those are obtained, respectively, and a differencebetween the maximum value of these likelihood and a likelihood withrespect to the transmission data sequence of the decoded data sequence(in the example of FIG. 7, the data sequence that reaches the state 0)obtained by terminating the decoding process is obtained (steps S1 toS4).

If this likelihood difference is within a certain range (in the exampleof FIG. 8, within Δ), the selected decoded data sequence is outputted bytraceback and the error-detecting coding (CRC coding) is conducted(steps S5 and S6).

Since in this embodiment the word length of the CRC code is a fixedlength and a frame configuration that the transmission data is arrangedjust ahead of the CRC code is adopted, (assumed) transmission data(part) and the (assumed) error-detecting code (part) for the assumedfinal bit position can be obtained. That is, by assuming the final bitposition, the transmission data (part) and the error-detecting code(part) are concomitantly assumed. Then, the obtained (assumed)transmission data undergoes the error-detecting (re-)coding (CRCcoding).

If this re-coded CRC agrees with the received CRC ((assumed)error-detecting code), the decoding is ended and the transmission datais acquired (restored) by deciding that the assumed final bit positionis the final bit position of the transmission frame data. Since the bitarrangements of the transmission data in the frame and of theerror-detecting code are in a reverse order to each other, theprobability that a comparison result of CRCs indicates coincidenceerroneously is extremely small.

If the likelihood difference exceeds Δ or the comparison result of CRCsindicates no coincidence, a next position is assumed and Viterbidecoding is continued. In addition, if there are detected a plurality ofpositions where the likelihood difference is within Δ and the comparisonresult of the error-detecting codes indicates coincidence when Viterbidecoding and the calculation of the error-detecting code are conductedfor the assumed final bit positions, a decision that a position wherethe likelihood difference becomes the minimum is the final bit positionof the transmission frame data may be made. This will be describedlater.

In the example of FIG. 7, if no error occurs on the way of transmission,it is reasonable to think as follows: a sequence that reaches the state0 at the second position (L=2) has the maximum likelihood (likelihooddifference=0) and the comparison result of the error-detecting codes forthis decoded sequence indicates coincidence.

On the other hand, if an error or errors occurs on the may oftransmission, a sequence that reaches the state 0 does not necessarilyhave the maximum likelihood. Accordingly, by setting Δ to an appropriatevalue, the same effect of reduction in the rate-decision error rate asthat in the case of no transmission error can be obtained also for thedecoded sequence such that occurred errors have been corrected. In aregion where the value of Δ is not more than a certain value, by settingΔ to a smaller value, an average rate-decision error rate can be loweredfurther; an average frame error rate (the probability that thecomparison result of CRCs indicates no coincidence+the rate-decisionerror rate) becomes larger.

Therefore, for example, for data that requires an extremely lowrate-decision error rate, such as control data, it is better to make Δsmaller at the cost of the frame error rate to some degree.

Alternatively, considering tendency of the errors that occur during thetransmission with respect to Δ, the difference between the maximum andthe minimum of the likelihoods obtained at respective assumed final bitpositions is regarded as a factor and a constant value multiplied bythis factor may be set as Δ.

If the re-coded CRC does not match the received CRC at all the assumedfinal bit positions, it is decided that there is no transmission data orthe received frame data contains an error.

When data transmission is conducted using the transmitter and thereceiver of such configurations as in the foregoing, even if thereceiving side varies the number of bits in the frame (namely, apparenttransmission rate) without sending any information indicating the numberof transmission bits in the frame from the receiving side, the receivingside can receive the data.

In addition, this scheme makes it possible both, at the receiving side,to lower the probability of detecting the rate mistakenly duringtransmitting the variable rate data, and at the transmitting side, toeliminate the need for providing buffer for temporarily storing thetransmission data.

Furthermore, by adopting the rate decision method that uses jointly thelikelihood information during Viterbi decoding, it is possible to lowerthe possibility of outputting the transmission data of an erroneouslength in the frame on the basis of the erroneous decision result of therate, and thus a highly-reliabile variable rate data transmission can beconducted.

Because the error-detecting code is not transmitted for a frame withouttransmission data, overhead can be reduced.

As described above, if there are detected a plurality of positions wherethe likelihood difference is within Δ and the comparison result of theerror-detecting codes indicates coincidence when Viterbi decoding andthe calculation of the error-detecting code are conducted for theassumed final bit positions, a decision that a position where thelikelihood difference becomes the minimum is the final bit position ofthe transmission frame data may be made.

FIGS. 9A and 9B show another example of the processing of rate decision(algorithm). In the example of FIGS. 9A and 9B, —representing theassumed bit position as L—an assumed first position (L=1) through anassumed final position (at step S31, whether or not the assumed finalposition has been checked is judged) are thoroughly checked and then adecision that a position where the likelihood difference is the minimumis the final bit position is made. In this occasion, a variable S_(min)for storing the minimum likelihood difference and a variable L′ forstoring its position are used.

However, it is conceivable that there is a case where the likelihooddifference is within Δ and not a single position where the comparisonresult of the error-detecting codes indicates coincidence is detected.Since in that case, even at the stage of step S33, L′ satisfies L′=−1 (avalue that was set at step S21), it is decided that there is notransmission data or the received frame data contains an error. Inaddition, if the value of Δ is set to infinity, a situation that not asingle position where the likelihood difference is within Δ is detectedcan be avoided.

In this embodiment, the error-correcting coding is conducted with aconvolutional code, but the error-correcting coding may be done by meansof other method, for example, one with a turbo code. Furthermore, as theabove-mentioned WO97/50219, the frame data may be divided into aplurality of blocks and each block may undergo the error-correctingcoding with a block code.

Moreover, in this embodiment, the frame data undergoes theerror-correcting coding and the interleaving as well as thedeinterleaving and the error-correcting decoding. However, without theseoperations, it is possible that the probability of detecting the ratemistakenly in the variable rate data transmission is suppressed to lowand that the need for providing buffer for temporarily storing thetransmission data is eliminated. In that case, all that is needed isthat among the assumed final bit positions of the assumed frame data, aposition where the assumed error-detecting code agrees with anerror-detecting code calculated on the basis of the assumed transmissiondata is simply decided to be the final bit position of the frame data,without using the likelihood information.

If it is known that the length of transmission data is one of twovalues, X (X≠0) and 0, then the process on the receiving side can befurther simplified. That is, it is not required that every final bitpositions be successively assumed in each frame. Instead, thetransmission data (length: X) and the error-correcting code aredetermined based on the final bit position determined with respect tothe length, X, of the transmission data and the error-detecting code ofthe determined transmission data is calculated. If the determinederror-detecting code matches the calculated error-detecting code basedon the determined transmission data, it is decided that there istransmission data. Otherwise, it is decided that there is nottransmission data or the received frame data contains an error.

(Second Embodiment)

FIGS. 10A and 10B show examples of the block constructs of a transmitterand a receiver in a second embodiment according to the presentinvention.

In the configuration of FIGS. 10A and 10B, transmission of informationindicating the rate of the transmission data is added to theconfiguration of FIGS. 3A and 3B, and the receiving side uses this rateinformation additionally to make the rate decision. In FIGS. 10A and10B, all the parts common to those of the configurations of FIGS. 3A and3B are denoted by the same numerals. Description of operations will begiven below, focusing on parts different from those of FIGS. 3A and 3B.

First, information (transmission rate information) indicating thetransmission rate of the transmission data applied to terminal 5 is sentto rate information memory 40. Here, the contents of the rateinformation memory 40 are rate information about the transmission data,namely, the number of bits. A multiplexer 6′ outputs the followinginformation successively frame by frame: information indicating the rateof the transmission data red from the rate information memory 40; thetransmission data sent from terminal 1, an error-detecting codecalculated for the transmission data in error-detecting coder 4; and thetail bits. The multiplexer 6′ outputs neither the transmission data,error-detecting code, nor tail bit if a frame contains no transmissiondata, instead, it outputs only the transmission rate information. Alsoin this embodiment, the error-detecting code is arranged after thetransmission data and the bits of the error-detecting code are arrangedin the opposite order to the transmission data. In this embodiment, thetransmission rate information is provided at the head of the frame.

Also in this embodiment, the sum of the length of the transmission dataand the length of the error-detection code (CRC bits) in one frame is4096 bits maximum. The length of the error-detecting code is 16 bits.Other values may be set as the maximum length of the transmission dataand length of the error-detecting code.

FIGS. 11A, 11B and 11C show examples of the data sequence output fromthe multiplexer 6′. FIG. 11A shows the case where the transmission rateof the transmission data is the maximum, 11B shows the case where thetransmission rate is below the maximum rate and there is transmissiondata, and FIG. 11C shows the case where there is no transmission data.

In this embodiment, the error-correcting coder 8 conducts theerror-correcting coding with a block code for the transmission rateinformation (as examples of concrete error-correcting codes, one mayenumerate a double orthogonal code, Reed-Muller code, BCH code, etc. oralternatively error-correcting coding other than the error-correctingcoding with a block code may be used), and does the error-correctingcoding with a convolutional code for the transmission data, theerror-detecting code, and the tail bits. Furthermore, the interleaver 10conducts the interleaving of these data that have undergone theerror-correcting coding, either independently for each data orcollectively. In addition, in the error-correcting coder 8, all of thetransmission rate information, the transmission data, theerror-detecting code, and the tail bits may undergo collectively theerror-correcting coding with a convolutional code.

On the other hand, in the receiver, if the transmission rate informationundergoes the error-correcting coding with a block code or the likeindependently from the transmission data or the like, the transmissionrate information part undergoes the error-correcting decoding properlyin an error-correcting decoder 26′ and subsequently the decoding resultis retained in a rate information memory 42. On the contrary, if thetransmission rate information, the transmission data, etc. undergoconvolutional-coding collectively, in the error-correcting decoder 26′the decoding result of the rate information bits part arranged at thehead of the frame is temporarily obtained by interrupting sequentialViterbi decoding that has been started from the head of the frame, andthis decoding result is retained in the rate information memory 42.

FIG. 12 shows the rate decision processing (algorithm) in the receiverof this embodiment. The error-correcting decoder 26′ assumes a positionindicated by the contents of the rate information memory 42 as the finalbit position, continues to conduct Viterbi decoding of the frame data upto that position, outputs the decoded data sequence obtained byterminating the decoding process through traceback, and conducts theerror-detecting coding (CRC coding) (steps S11 to S15).

If the re-coded CRC agrees with the received CRC the decoding process iscompleted (step S16), a decision that the position indicated by thecontents of the rate information memory is the final bit position of thetransmission frame data is made and the transmission data is acquired(restored). Since the bit arrangements of the transmission data in theframe and of the error-detecting code are set in a reverse order to eachother, the probability that the comparison result of CRCs indicatescoincidence erroneously is extremely small.

In this embodiment, if the comparison result of CRCs indicates nocoincidence, the final position of the transmittable frame data otherthan the final bit position indicated by the contents of the rateinformation memory is assumed successively, the error-correctingdecoding and the calculation of the error-detecting code are conducted,and the rate decision is made using the likelihood information duringViterbi decoding and the comparison result of the error-detecting codes(the same processing as step S17 and steps S1 to S8 of FIG. 8).

Also, between steps S13 and S14, similarly to the first embodiment, thefollowing steps may be added: determining the maximum likelihood (stepS3); finding the likelihood difference (step S4); and judging whether ornot the likelihood difference is within a certain range (step S5).Concrete processes may be as follows: if the likelihood difference iswithin a certain range, the flow is made to proceed to step S14; if thelikelihood difference is not within a certain range, the flow is made toproceed to step S17. In the case where such processing (steps S3 to S5)is conducted, although the number of processes increase as compared towhen such processing is not done, the rate-decision error rate can beimproved further. In addition, Δ used at step S5 between step S13 andstep S14 and Δ used at step S5 while being in step S17 may be the samevalue or may be different values.

If the re-coded CRC does not match the received CRC at all the assumedfinal bit positions, it is decided that there is no transmission data orthe received frame data contains an error.

Also in the case where the transmitter and the receiver of the foregoingconfigurations are used to conduct the data transmission, it is possiblethat the probability of detecting the rate mistakenly at the receivingside during transmitting variable rate data is suppressed to low andthat the need for providing buffer for temporarily storing thetransmission data at the transmitting side is eliminated.

Moreover, if there is no transmission error, the rate information issurely detected by the receiver; on the other hand, supposing that therate information is transmitted erroneously, the rate decision is madepossible through the use of likelihood information during Viterbidecoding and the comparison result of the error-detecting codes, so thatthe final frame error rate is improved and a low rate-decision errorrate is achieved. By this means, the highly-reliabile variable rate datatransmission can be performed.

Because the error-detecting code is not transmitted for a frame withouttransmission data, overhead can be reduced.

In addition, since the reliability of Viterbi decoding result of therate information bit part can be made larger as the input signal storedin the decoder, namely, the length of the subsequent coded data sequencebecomes longer in the foregoing description, it is preferable that thedata sequences of a fixed length other than the transmission data, suchas the error-detecting code, are arranged just after the rateinformation bits successively as much as possible.

Alternatively, it may be also possible that in the transmitter the tailbits are inserted after the rate information bits, and in the receiverthe decoding operation is temporarily completed at this tail bits, andafter the received rate information is obtained, the decoding operationis re-started to decode the frame data up to the final bit.

Also in this embodiment, if it is known that the length of transmissiondata is one of two values, X (X≠0) and 0, then the process on thereceiving side can be further simplified. That is, if the rateinformation indicates a transmission data length of 0 at step S12 inFIG. 12, it is determined that there is no transmission data, and thenthe process ends. If the rate information indicates a transmission datalength of X, the process at step S13 and the subsequent steps isperformed, and if the received CRC matches the re-coded CRC at step S16,it is decided that there is transmission data, otherwise, it is decidedthat there is no transmission data or the received frame data containsan error.

Alternatively, even if the rate information indicates a transmissiondata length of Y (Y≠0, Y≠X) (in such a case, the rate information iswrong), the transmission data and error-detecting code (received CRC)may be determined based on the final bit position determined on theassumption that the length of the transmission data is X, theerror-detecting code (re-coded CRC) of the determined transmission datamay be calculated, and if the received CRC matches the re-coded CRC, itmay be decided that there is transmission data, otherwise it is decidedthat there is no transmission data or the received frame data containsan error.

Moreover, even if the rate information indicates at transmission datalength of Y=0, the transmission data and error-detecting code (receivedCRC) may be determined based on the final bit position determined on theassumption that the length of the transmission data is X, theerror-detecting code (re-coded CRC) of the determined transmission datamay be calculated, and if the received CRC matches the re-coded CRC, itmay be decided that there is transmission data, otherwise, it is decidedthat there is no transmission data or the received frame data containsan error.

In the first and second embodiments, it is possible that in judging (atthe receiving side) whether or not the likelihood difference is withinthe predetermined range (step S5 in FIG. 8), the predetermined range(the value of Δ in FIG. 8) is varied (is made different) according tothe assumed final bit position of the frame data.

When the present invention is applied in actual radio communicationenvironments, a proper value of Δ to obtain the desired detectionperformance may differ for each of the final bit positions (that is,different number of bits of the transmitted data in the frame) dependingon the tendency of the transmission bit errors in the transmission path.In such cases, if a single value of Δ is used in common, the ratedetection performance differs according to the final bit position.Consequently, there arises a problem in that when a percentage oftransmission frequencies of the transmission rates (final bit positions)vary, the average quality of the variable rate data transmissionincluding the rate detection performance changes.

Then, it is conceivable that the value of Δ for the decision of thethreshold value is set to not a single value but several differentvalues (Δ1, Δ2, . . . ΔL, . . . , ΔN) for respective final bit positions(respective transmission rates) and thereby the decision of the rate ismade possible. Here, a value of each ΔL may be varied during thetransmission so as to be always an optimum value in response to thechange in the transmission environment. Furthermore, the same value maybe used in part repeatedly.

(Third Embodiment)

Transmission data for a plurality of channels can be multiplexed into(contained in) each frame and the data transmission method describedwith respect to the first or second embodiment can be applied to only(variable-length data of) some of the channels. For example, if achannel for transmitting a control signal is included in the channels tobe multiplexed, the method of the first or second embodiment may beapplied to only the control signal transmission channel.

FIG. 16 shows an example in which transmission data for two channels iscontained in one frame. In FIG. 16, the data transmission methoddescribed in the second embodiment is applied to one (a first) channelof the two channels. One of the data transmission methods (the method inthe second embodiment in which an error-detecting code is added even ifthere is no transmission data) described in WO00/79720, for example, isapplied to the other channel (i.e. a second channel). Alternatively, adata transmission method may be used in which a transmission rate isdetermined by using only transmission rate information without using(adding) the error-detecting code for the second channel. In addition,if the transmission data over the second cannel is fixed-length data, adata transmission method in which no transmission rate determination isconducted for the second channel.

In the example shown in FIG. 16, first, transmission rate informationabout the first channel (first transmission rate information) andtransmission rate information about the second channel (secondtransmission rate information) are placed in one frame. Then, a section(having a fixed length) allocated to the first channel and a section(having a fixed length) allocated to the second channel are provided andtransmission data, an error-detecting code, and a tail bit for eachchannel are contained in each allocated section. If the frame containsno transmission data for first channel, neither the transmission data,error-detecting code, nor tail bit is contained in the section allocatedto the first channel. The first and second transmission rate informationmay be contained in the respective sections allocated to the respectivechannels.

The transmission rate information about the channels may be combinedinto one piece of transmission rate information.

FIG. 17 shows the case where two sets of transmission rate informationshown in FIG. 16 are combined into one transmission rate information. Itis assumed that the transmission rate of the first channel can be one offive rates, 0 kbps, 10 kbps, 20 kbps, 30 kbps, and 40 kbps, and thetransmission rate of the second channel can be one of three rates, 0kbps, 50 kbps, and 100 kbps, for example. In this case, if separateitems of transmission rate information as shown in FIG. 16 were used, 3bits would be required for the first transmission rate information and 2bits would be required for the second transmission rate information,thus requiring a total of 5 bits for the transmission rate information.On the other hand, if the combined transmission rate information asshown in FIG. 17 is used, the first channel transmission rate/secondchannel transmission rate can be indicated with one of 15 (=5×3)combinations, 0 kbps/0 kbps, 10 kbps/0 kbps, 20 kbps/0 kbps, . . . , 20kbps/100 kbps, 30 kbps/100 kbps, and 40 kbps/100 kbps, thus the combinedtransmission rate information requires only 4 bits. Therefore, using thecombined transmission rate information has the advantage of reducingoverhead.

The transmission rate information about the first channel or secondchannel alone may be sent, or no transmission rate information (aboutboth of the channels) may be sent. For example, the first channeltransmission rate information is not sent and the method (transmissionwithout transmission rate information) of the first embodiment may beused for the first channel instead of the method of the secondembodiment (transmission with transmission rate information). If thesecond channel transmission rate information is not sent, one of themethods described in WO00/79720 (the method in the first embodiment inwhich an error-detecting code is added even if there is no transmissiondata) for example, may be used for the second channel.

The transmission rate information about all or none of the channels maybe sent depending on the circuitry of a transmitter/receiver. This isbecause: there is the case where an error-correcting code (for exampleblock coding) is also applied to transmission rate information and theerror correction capability of the error-correcting coding (for example,convolutional coding) for a part containing an error-detecting code isrelatively high (that is, the transmission quality of the transmissionrate information is relatively low) and, in such a case, the errordetection precision can be increased by detecting a transmission rate byusing the error-detecting code without the help of the transmission rateinformation even if it is available. Here, if combined transmission rateinformation is used, it may not be required that the combinedtransmission rate information contain information about the transmissionrate of a channel to which the method of the second embodiment isapplied. If the combined transmission rate information does not containthe first channel transmission rate in the above-described example, thecombined transmission rate information will consist of only the secondchannel transmission rate information, thus requiring only 2 bits.However, it is not always advantageous to over-refine a transmissionformat (to use a variable format) so as to transmit only a requirednumber of transmission rate information bits, because it would generallycomplicate circuitry.

While the example has been described in which the method of the first orsecond embodiment is applied to one channel and none of them are appliedto another channel, the method of first or second embodiment may beapplied two or more channels or none of them may be applied to two ormore channels.

The error-correcting coding may be performed by block coding the part oftransmission rate information and convolutional coding the sectionallocated to each channel. The convolutional coding may be applied tothe part of the transmission rate information as well. In this case, theconvolutional coding may be applied to the transmission rate informationand the section allocated to the first channel separately orcollectively.

(Fourth Embodiment)

Dual closed loop transmission power control comprising inner looptransmission power control and outer loop transmission power control maybe applied to data transmission in the third embodiment. One or morechannels other than channels to which the method of the first or secondembodiment is applied may be used as the reference of the outer looptransmission power control (hereinafter simply called “controlreference”).

For example, if channels to be multiplexed include a control signaltransmission channel, the control signal transmission channel is notused as the control reference, instead, one or more of channels otherthan that channel may be used as the control reference. A control signaltransmission channel cannot precisely provide outer loop transmissionpower control (block or frame error-rate quality maintenance control)based on, for example, the result of decision of a received CRC as thecontrol reference, because information is generally transmittedintermittently.

The outer loop transmission power control is performed on the assumptionthat inner loop transmission power control is performed simultaneously.In particular, the outer loop transmission power control adjusts atarget SIR (signal-to-interference-and-noise ratio) used for the innerloop transmission power control so that a frame (block) error ratequality, which is separately measured at the receiving side, becomes itstarget value. Inner loop transmission power control herein is control inwhich a receiving side compares the received SIR of a received signalwith a predetermined (target) SIR, and if the received SIR is below thetarget SIR (that is, the received quality is below the target quality),sends a control signal to the sending side to cause it to increase thetransmission power, and, if the received SIR exceeds the target SIR(that is, the received quality exceeds the target quality), sends acontrol signal to the sending side to cause it to reduce thetransmission power.

In general, outer loop transmission power control (is dual closed loopcontrol and) controls transmission power moderately compared with innerloop transmission power control. If a plurality of channels aremultiplexed and a target frame (block) error rate quality is set foreach channel, the target SIR used for the inner loop transmission powercontrol is adjusted so as to satisfy all the target frame (block) errorrate qualities.

The relative ratio between error-correcting coding ratios of themultiplexed channels and the relative ratio between transmission powersfor the multiplexed channels can be fixed. The relative ratios may bedecided in consideration of the required quality of each channel.

When the transmission power of the reference channel is determined bythe outer loop transmission power control, the transmission powers ofthe other channels are also determined in the case where the relativeratios of the transmission powers are fixed. That is, the transmissionpowers of the channels other than the reference channel can becontrolled indirectly.

In some cases, the transmission power of a channel may be changedaccording to its rate. In such a case, for example the relative ratio Qbetween the transmission power of a reference channel during thetransmission at the maximum rate R_(1,M) and the transmission power of achannel other than the reference channel during the transmission at themaximum rate R_(2,M) is set at a fixed value. Let the relative ratiobetween the transmission power of the reference channel duringtransmission at a certain rate R_(1,J) and the transmission power duringtransmission at the maximum rate R_(1,M) be S(R_(1,J)), and the relativeratio between the transmission power of the non-reference channel duringtransmission at a certain rate R_(2,K) and the transmission power duringthe transmission at the maximum rate R_(2,M) be S(R_(2,K)). If thetransmission power of the reference channel during the transmission atrate R_(1,J) is determined to be P_(1,J) then the transmission powerP_(2,K) of the non-reference channel during the transmission at rateR_(2,K) can be determined by P_(1,J)×Q×S (R_(2,K)) /S(R_(1,J)).

(Others)

The techniques described in the first through fourth embodiments may beapplied both to the case of “postposition and same order” (that is, acase where the error-detecting code is arranged after the transmitteddata and the bit arrangements of the transmitted data and of theerror-detecting code are set in the same order) and to the case of“preposition” (that is, a case where the error-detecting code isarranged ahead of the transmitted data and the bit arrangements may bein the same order or in a reverse order).

FIGS. 13A, 13B and 13C show examples of the frame configurations of thetransmission data in the case of “postposition and same order” and FIGS.14A, 14B and 14C show examples of the frame configurations of thetransmission data in the case of “preposition”. FIGS. 13A and 14A showcases where the transmission rate of the transmission data is at themaximum, FIGS. 13B and 14B show cases where the transmission rate isbelow the maximum rate and the frame contains transmission data, FIGS.13C and 14C show cases where the frame contains no transmission data.Configuration examples of the transmitter and the receiver used in thecase of “postposition and same order” and in the case of “preposition,”a processing example, and the like are the same as those described withrespect to the first through fourth embodiments. In addition, in thecase of “preposition,” as shown in FIGS. 15A and 15B, it is conceivablethat, for example a frame memory 40 is provided between the terminal 1and the multiplexer 6 and thereby the transmitted data is temporarilystored, and in the mean time the error-detecting code is calculated bythe error-detecting coder 4. Moreover, it is conceivable that, forexample, an error-detecting code memory 42 is provided between thedemultiplexer 28 and the comparator 34 and thereby the assumederror-detecting code is temporarily stored, and in the meantime theerror-detecting code of the assumed transmitted data is calculated bythe error-detecting coder 30.

According to the present invention as described above, high-qualityvariable-rate data transmission can be achieved based on a precise ratedetection while reducing overhead in accordance with the concept ofblind rate detection in which rate information is not transmitted.

The present invention has been described in detail with respect topreferred embodiments, and it will now be apparent from the foregoing tothose skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspect, and it isthe intention, therefore, in the apparent claims to cover all suchchanges and modifications as fall within the true spirit of theinvention.

1. A data transmission method for placing variable-length transmissiondata in each frame having a fixed time length to transmit the frame, alength of the transmission data being one of two values, X (X≠0) and 0,the data transmission method comprising the steps of: at a transmittingside, calculating an error-detecting code of the transmission data inthe frame only if the frame contains the transmission data; generatingframe data containing the transmission data and the calculatederror-detecting code of the transmission data if the frame contains thetransmission data, and generating frame data that contains neither thetransmission data nor the error-detecting code of the transmission dataif the frame does not contain the transmission data; and transmittingthe generated frame data; and at a receiving side, receiving the framedata; determining the transmission data and the error-detecting code ofthe transmission data by determining a predetermined position in thereceived frame data as the final bit position of the frame data, andcalculating an error-detecting code based on the determined transmissiondata; deciding that the frame contains the transmission data if thedetermined error-detecting code matches the error-detecting codecalculated based on the determined transmission data, and deciding thatthe frame data does not contain the transmission data or the receivedframe data contains an error if the determined error-detecting code doesnot match the calculated error-detecting code; and obtaining thetransmission data in the frame based on the result of the decision,wherein at the receiving side, the step of determining and calculatingdetermines the transmission data and the error-detecting code based onthe final bit position where the length of the transmission data is X,and calculates the error-detecting code based on the determinedtransmission data, and wherein, at the transmitting side, the step ofgenerating the frame data generates the frame data in which theerror-detecting code is placed after the corresponding transmission dataand the bits of the error-detecting code are arranged in the order thatis the reverse of the order of the bits of the transmission data.
 2. Adata transmission method for placing variable-length transmission datain each frame having a fixed time length to transmit the frame, a lengthof the transmission data being one of two values, X (X≠0) and 0, thedata transmission method comprising the steps of: at a transmittingside, calculating an error-detecting code of the transmission data inthe frame only if the frame contains the transmission data; generatingframe data containing the transmission data and the calculatederror-detecting code of the transmission data if the frame contains thetransmission data, and generating frame data that contains neither thetransmission data nor the error-detecting code of the transmission dataif the frame does not contain the transmission data; and transmittingthe generated frame data; and at a receiving side, receiving the framedata; determining the transmission data and the error-detecting code ofthe transmission data by determining a predetermined position in thereceived frame data as the final bit position of the frame data, andcalculating an error-detecting code based on the determined transmissiondata; deciding that the frame contains the transmission data if thedetermined error-detecting code matches the error-detecting codecalculated based on the determined transmission data, and deciding thatthe frame data does not contain the transmission data or the receivedframe data contains an error if the determined error-detecting code doesnot match the calculated error-detecting code; and obtaining thetransmission data in the frame based on the result of the decision,wherein at the receiving side, the step of determining and calculatingdetermines the transmission data and the error-detecting code based onthe final bit position where the length of the transmission data is X,and calculates the error-detecting code based on the determinedtransmission data, wherein the data transmission method multiplexesvariable-length transmission data for channels in a first channel groupof one or more channels and transmission data for channels in a secondchannel group of one or more channels into each frame having a fixedtime length to transmit the frame, and wherein at the transmitting side,the step of calculating the error-detecting code calculates, for eachchannel in the first channel group, the error-detecting code of thetransmission data only if the frame contains the transmission data forthat channel; the step of generating the frame data generates, for eachchannel in the first channel group, partial frame data containing thetransmission data for the channel and the calculated error-detectingcode of the transmission data for the channel if the frame contains thetransmission data for the channel, and generates, for each channel inthe first channel group, partial frame data containing neither thetransmission data for the channel nor the error-detecting code of thetransmission data for the channel if the frame does not contain thetransmission data for the channel; and the step of transmitting theframe data transmits the whole frame data containing the generatedpartial frame data for each channel in the first channel group, andwherein at the receiving side, the step of receiving the frame datareceives the whole frame data; the step of calculating theerror-detecting code determines the transmission data for each channelin the first channel group and the error-detecting code of thetransmission data for the channel by determining a predeterminedposition in the partial frame data for the channel contained in thereceived whole frame data as the final bit position and calculates anerror-detecting code based on the decided transmission data for thechannel; the step of deciding decides, for each channel in the firstchannel group, that the partial frame data for the channel contains thetransmission data for the channel if the determined error-detecting codeof the determined transmission data for the channel matches theerror-detecting code calculated based on the determined transmissiondata for the channel, and decides, for each channel in the first channelgroup, that the frame does not contain the transmission data for thechannel or the partial frame data for the channel contains an error ifthe determined error-detecting code of the determined transmission datafor the channel does not match the error-detecting code calculated basedon the determined transmission data for the channel; and the step ofobtaining the transmission data obtains the transmission data for eachchannel in the first channel group in the frame based on the result ofthe decision.
 3. A data transmission method for placing variable-lengthtransmission data in each frame having a fixed time length to transmitthe frame, comprising the steps of: at a transmitting side, calculatingan error-detecting code of the transmission data in the frame only ifthe frame contains the transmission data; generating frame datacontaining the transmission data and the calculated error-detecting codeof the transmission data if the frame contains the transmission data,and generating frame data that contains neither the transmission datanor the error-detecting code of the transmission data if the frame doesnot contain the transmission data; and transmitting the generated framedata; and at a receiving side, receiving the frame data; assuming thetransmission data and the error-detecting code of the transmission databy assuming one or more final bit positions of the received frame data,and calculating an error-detecting code based on the assumedtransmission data; deciding a position to be the final bit position ofthe frame data if there is the position in the frame where the assumederror-detecting code matches the error-detecting code calculated basedon the assumed transmission data among the assumed final bit positionsof the frame data, and deciding that the frame does not contain thetransmission data or the received frame data contains an error if thereis no position where the assumed error-detecting code matches thecalculated error-detecting code; and obtaining the transmission data inthe frame based on the result of the decision, wherein the datatransmission method multiplexes variable-length transmission data forchannels in a first channel group of one or more channels andtransmission data for channels in a second channel group of one or morechannels into each frame having a fixed time length to transmit theframe, and at the transmitting side, the step of calculating theerror-detecting code calculates the error-detecting code of thetransmission data for each channel in the first channel group only ifthe frame contains the transmission data for the channel; the step ofgenerating the frame data generates, for each channel in the firstchannel group, partial frame data containing the transmission data forthe channel and the calculated error-detecting code of the transmissiondata for the channel if the frame contains the transmission data for thechannel, and generates, for each channel in the first channel group,partial frame data containing neither the transmission data for thechannel nor the error-detecting code of the transmission data for thechannel if the frame does not contains the transmission data for thechannel; and the step of transmitting the frame data transmits the wholeframe data containing the generated partial frame data for each channelin the first channel group, and at the receiving side, the step ofreceiving the frame data receives the whole frame data; the step ofcalculating the error-detecting code assumes the transmission data foreach channel in the first channel group and the error-detecting code ofthe transmission data for the channel by assuming one or more final bitpositions of the partial frame data for the channel contained in thereceived whole frame data and calculates an error-detecting code basedon the assumed transmission data for the channel; the step of decidingdecides, for each channel in the first channel group, a position to bethe final bit position of the partial frame data for the channel ifthere is the position where the assumed error-detecting code of thetransmission data for the channel matches the error-detecting codecalculated based on the assumed transmission data for the channel amongthe assumed final bit positions of the partial frame data for thechannel, and decides, for each channel in the first channel group, thatthe frame does not contain the transmission data for the channel or thepartial frame data for the channel contains an error if there is noposition where the assumed error-detecting code of the transmission datafor the channel matches the error-detecting code calculated based on theassumed transmission data for the channel among the assumed final bitpositions of the partial frame data for the channel; and the step ofobtaining the transmission data obtains the transmission data for eachchannel in the first channel group in the frame based on the result ofthe decision.
 4. The data transmission method as claimed in claim 2 or3, wherein dual closed loop transmission power control comprising innerloop transmission power control and outer loop transmission powercontrol is performed for the data transmission between the transmittingside and the receiving side and one or more channels in the secondchannel group are used as the reference for the outer loop transmissionpower control without using channels in the first channel group as thereference.
 5. The data transmission method as claimed in claim 4,wherein the relative ratio between error-correcting coding ratios of themultiplexed channels and the relative ratio between transmission powersfor the multiplexed channels are fixed.